A wide variety of magnetic read-write head structures exists. Among these, the structures which are adapted for both reading and writing employ one of several technologies such as inductive, magneto-resistive or other solid state (Hall or magnetic transistor) sensors. The preferred embodiment described herein addresses several problems with the known prior art.
Little is known as to any prior twin track reading and writing head structures or techniques. The most similar read-write head structures are generically different from those presented in this application but a brief review of them is offered as an aid to understanding the present invention.
U.S. Pat. No. 4,413,296 illustrates a single track read head employing a thin film magneto-resistive sensing element. In this structure, no means is provided for establishing and maintaining an anti-parallel magnetic couple having the preferred magnetization orientation directed along the easy axis of the MR films. This means that unless single domain magnetic films are employed, Barkhausen noise will be present from the shifting multi-domain walls. The Barkhausen noise effect is a particularly significant problem as will be appreciated by those of skill in the art. Furthermore, the difficulties in establishing a single domain magnetic film are technically prohibitive at present. In addition, in structures such as that shown in the aforementioned patent, demagnetizing fields are automatically created in both films whenever external magnetic fields are applied along either the X or Y axis. The demagnetizing fields will be evident at the edges or ends of the films and will tend to create multi-domain walls with the attendant increase in Barkhausen noise. As the relative size of such sensors is reduced to accommodate smaller recording tracks with the consequent higher density, the effects of the Barkhausen noise become overwhelmingly important.
Another typical prior art sensor that has the advantage of providing a differential signal output is shown in the U.S. Pat. No. 3,860,965, commonly assigned to the assignee hereof. While this structure exhibits significant advantages in having a differential output, no means is provided for establishing the anti-parallel couple within the twin films in a direction of preferred magnetization oriented along the easy axis. Again, the problem of multi-domain walls shifting and creating Barkhausen noise is present. In addition, demagnetizing fields will be introduced in both films whenever an external field is applied along either the X or Y axis; the effect of the demagnetizating fields is to reduce the signal output available and to encourage the formation of multi-domain walls with the concommitant result of increased Barkhausen noise.
A further problem with known prior art magneto-resistive or inductive or solid state magnetic read-write head structures is that the sensor element must often be placed in very close proximity to the magnetic record in order to experience enough magnetic flux to provide a usable output. This results in problems with head to recording medium contact and wear problems well known to those skilled in the field. It would be desirable to remove the sensitive element to an elevation above the recording medium without reducing the sensitivity thereof.